Height-adjustable school blackboard



Oct. 18, 1966 JENNY ET AL HEIGHT-ADJUSTABLE SCHQOLVBLACKBOARD 5Sheets-Sheet 1 Filed D80. 5, 1963 INVENTORS HANS JENNY BY MAX ALTMANNOct. 18, 1966 JENNY ETAL HEIGHT-ADJUSTABLE $05001. BLACKBOARD 5Sheets-Sheet 5 Filed D90. 5, 1963 INVENTORS HANS JENNY BY MAX ALTMANNUnited States Patent 3,279,101 HEIGHT-ADJUSTABLE SCHOOL BLACKBOARD HansJenny, Niederurnen, and Max Altmann, Niederwen ingen, Switzerland,assignors to Firma Palor AG., Niederurnen, Saint Gallen, SwitzerlandFiled Dec. 3, 1963, Ser. No. 327,598 Claims priority, applicationSwitzerland, Dec. 4, 1962, 14,211/62; Nov. 16, 1963, 14,069/63 6 Claims.(Cl. 35-63) School blackboards satisfying teaching requirements havealready been known for some time. In order to make use of the availablewriting surface, they are made vertically adjustable, and furtherarranged to be movable so far down that the rearward wall surface can beexposed for the attachment of a projection screen. These known schoolblackboards not only have technical deficiences but also decisiveeconomical disadvantages.

The black-boards themselves are made partly of wood and partly ofasbestos cement panels; the writing surface of the latter is coated witha baked varnish; this has been found particularly durable since it doesnot wear away and thus retains its original, good properties, even aftermany years of use. The asbestos cement panels to be used must not bethicker than about 2.3 millimeters, since thicker panels are too heavy.These panels, however, are brittle and very sensitive to shocks andblows. Consequently, it frequently happens that such blackboard surfacesbecome damaged or partially useless during lessons or duringintermission, by pressure, shocks or blows.

Hitherto it has been endeavored to remedy this by the use of reinforcingmeans, for instance a slatted background structure, intended to givesupport to the thin asbestos cement panel.

The assembly and fitting of such slatted backgrounds is, however,complicated and laborious. Such a reinforcement has also been foundinadequatefor instance, the parts of the panel between the individualslats are particularly exposed. Hitherto, it has not been possible toobtain an absolutely plane writing surface, since the glue applied tothe frame and slat elements, wraps the panel when drying.

The school blackboards described are held in frames consisting of a Tbar as the top frame member, an angle bar as the bottom frame member,and two or more Z-bars serving as connecting members and guide rails; inaddition, there are the junction pieces for the substructure of theblackboard, the chalk ledge, and the rear wall. In order to give thisframe some degree of stiffness, all the parts mentioned must be solidlywelded together. This results in a shapeless, massive structurerequiring much labor to produce, and diflicult to transport. Inpractical use it has further been found that despite the many weldedjoints, lateral displacements bringing the whole structure out ofalignment can occur, and steady and undisturbed motion of theheight-adjustable blackboard cannot be attained. Moreover, it has notproved possible to obtain a plane frame for the blackboard itself whichwould remain so indefinitely. Such a frame for height-adjustableblackboards thus requires great care as to its construction andfunctioning.

Blackboard carriers '(easels) which have to receive not only the frameand the board itself, but also the means for vertical-1y displacing thecomplete blackboard, at present likewise consist of a large number ofindividual parts which must be screwed or welded together in acomplicated and tedious manner. This is the source of difficultyremediable defects. Similarly, the arrangement for the verticaldisplacement of the complete blackboard which is required to ensure asmooth and undisturbed action of the corresponding elements cannotfulfill these conditions.

3,279,101 Patented Oct. 18, 1966 In the known school blackboards eachcarrier consists of 8-10 separate parts, which are partly screwedtogether, but in most instances are welded and finished in place. Thevertical adjusting motion of such blackboards is as a rule performed bya device such as first described by applicants in their own Swiss Patent331,795 of March 18, 1955. This seeks to obtain an elastic support ofguide rollers running in rails in such manner that each guide roller isrotatably carried on a screw bolt, which itself is screwed verticallyinto a cylindrical sliding block disposed in a recess and influenced bya spring, intended to hold the sliding block, screw bolt and guideroller elastically against the guide rail. This spring consequently actsto force the screw bolt out of its position at right angles to thesliding block and thus cause the latter to jam in the recess, i.e. itsaction is retarding or jamming rather than controlling. The range ofaction of such a device is closely restricted. Finally, it attractschalk and schoolroom dust, which cannot be removed since after assemblyin the factory the device is no longer accessible. The blackboardtherefore becomes increasingly difiicult or ultimately impossible tomove.

The defects described are the cause of considerable economicdisadvantages. The blackboards have to be delivered to the place of usein two lots. The first lot comprises the blackboard underframe orcarrier with the actuating mechanism and the control elements thereof.Both lots include bulky and heavy pieces which must travel as bulkygoods. To these must be added, depending on the size of the blackboard,a counterweight of -150 kilograms for balancing the blackboard suspendedin its actuating mechanism, which has also to be transported. The totaltransport costs incurred are so high that the sale and delivery of suchblackboards to remote are-as is no longer practicable. This restrictionto a small consumer region also reduces the possible volume of sales,since new blackboards are only acquired for new or rebuilt schools orthe like. New means have therefore to be sought to overcome theseeconomic restrictions as well as to eliminate the technical drawbacks.

The object of the invention therefore is a height-adjustable schoolblackboard characterized in that it has a metalreinforced ready to useblackboard body, a non-warping blackboard frame which cannot be mountedin a wrong manner, a device enabling undisturbed vertical motion of theblackboard controlled by rotary clamps; and a cont-ainer filled with afinely-granular compound for balancing the weight of the blackboard.

An exemplary form of embodiment of the invention is shown in thedrawing, in which are represented:

FIG. 1a partial front view and a partial section of a blackboard body;

FIG. 2-a partial section along the line II of FIG. 1 on a slightlylarger scale;

FIG. 3the front view of the left-hand side of a blackboard frame;

FIG. 4a top view of FIG. 3; and

FIG. 5a side view;

FIG. 6-the side view of a blackboard underframe or carrier with rotaryclamps and travelling roller; and, further to FIG. 6-

FIG. 7a side view; and

FIG. 8- a top view.

In accordance with FIGS. 1 and 2, 1 is a blackboard panel of asbestoscement, of a thickness of about 2.2 millimeters, the front side whereofhas a writing surface of baked varnish. On its rear side it isreinforced by a sheet metal plate 2 of about 0.3 millimeters thicknesswhich is cemented thereon; for larger blackboard sizes this backingsheet is divided into separate panels, with expansion joints 3. The twofirmly-attached panels 1 and 2 are then attached on a wooden frame 4,which may also be effected by cementing or glueing.

Blackboard bodies of this construction have an absolutely andpermanently plane writing surface on which the wooden frame glued on theback is not apparent; it can be more closely and freely written on withchalk, owing to the counter-pressure of the backing sheet 2. The shockand impact resistance of the writing surface is practically unlimited.Tests at the Federal Establishment for Testing Materials,Zurich-Diibendorf, have shown that an asbestos-cement panel of 2.2millimeters having a permanent baked-on writing surface and a cementedbacking plate of 0.3 mm. thickness, withstands the impact of a weight of1 kilogram on an area of 0.5 cm. dropped from a height of 1 meter on thewriting surface of the freely supported blackboard body, withoutexperiencing damage or showing visible impact marks. A further,substantial advantage is that the board reacts elastically to the impactoftest balls, as the experimental series have shown. Yet another greatadvantage of such a metal-reinforced blackboard body is that magnetsapplied to the writing surface are attracted and held thereon. Themagnetic field penetrating the thin asbestos cement panel 1, issufficiently powerful for drawings, pictures, plans, etc. placed underthe magnets to be held on the board. The aforesaid Materials TestingEstablishment has also investigated this action of the blackboard body.The holding power of the magnets was found to be quite adequate for theobjects which are used for the purpose. In addition it was found that amagnet is 15-20% more strongly attracted by the metal sheet, when a 2.2mm. thick asbestos cement sheet is placed between the magnet and themetal sheet than when an air gap of the same thickness is left betweenthe magnet and the metal sheet. The metal reinforcement of theblackboard body is thus more effective in its action than the total ofthe individual elements. It will be clear that this offers quite new andunexpected posibilities for instructional purposes for the blackboardbody according to the invention.

The blackboard is transported as a thin piece so that space and expensesare saved.

At the place of use, the blackboard body 1-4 is assembled within ablack-board frame, as represented in FIGS. 3-5. This has as the topframe member a T bar 5, and as a lower frame member an angle bar 6, asWell'as connecting bars of Z-shape, 7 and 8, which latter also act asguide rails for the vertical motions of the blackboard. The T bar 5 andangle bar 6 form the horizontal frame members, and the connecting bars 7and 8 the vertical members thereof. The slide bars 9 and 10, as well asthe brackets 11 and 12 for the chalk ledge, are attached on the anglebar 6. The pair, associated angle plates, the so-called gusset plates 13and 14, and 15 and 16 respectively, are welded to the Z bars 7 and 8,staggered with respect to each other, and are attached to the horizontalframe members, the T bar 5 and the angle bar 6, during assembly attheplace of use, by at least 2 screws each. Inorder to obtain absolutelyflat or plane bearing surfaces for the blackboard body to be appliedthereon, the gusset plates 13-14'and 15-16 are screwed on the side ofthe blackboard frame opposite the writing surface, which can be quicklyand undetachably effected. They ensure the non-Warping rigidity of thecompleted blackboard frame. In the separate state, the individualmembers take up very little space during transportation, which againoffers considerable economic advantages.

Contrary to the known school blackboards, the blackboard carriers are inthis case of unit construction. In-

stead of a multiplicity of details which have to be welded or screwedtogether and usually require further work, a single workpiece is used,preferentially of castiron, to which only the controlling elements haveto be attached. FIGS. 6, 7 and 8 show such a blackboard carrier: 17 isits body, with the oval (oblong) holes 18 and 19 for its attachment bymeans of masonry bolts to the by a clamping screw 27 and counter-nut 28,is fitted,

which enables the pressure on the guide roller-24tobe controlled. Theguide roller 24 is pressed elastically against the guide rail 7 by theclamping lever assembly 22-29. The associated lower clamping lever worksin the same manner-see FIG. 6. As a rule, a single control unit with twoclamping levers sufiices for the blackboard carrier; .the other carriercan be equipped with guide rollers on fixed bearing pins.

The control assembly reliably functions indefinitely and has a play ofover 20 mm. which is large enough to compensate for any differencesarising either from the blackboard frame 5-16 or the blackboard body1-4, without the blackboard thereby shifting its position. At the sametime, a very elastic and smooth action of the vertical movements of theblackboard itself is obtained. H Finally, the control mechanism requiresno servicing, since the clamping lever and its bearing are insensitiveto dust, etc.

Finally, the problem of balancing the weight of the blackboard in motionis solved in a similarly simple manner. Instead ofan iron weight orweights of -150 kg, incurring high transportation costs'and labor. fortheir installation, the weight balancing the blackboard is a containerfilled with a mixture of finely granular1 material, which can usually beobtained locally. For this purpose, sand or a mixture of sand and gravelwill be found most suitable. These are easily procurable. and can bevery accurately weighed or measured. The empty container, which issimply a box, can at the same time be used for transporting assemblytools or the like.

The blackboard according to the invention is thus found to be a logicalassembly and a novel, interrelated solution of both the technical andthe economic problems involved. The individual elements are not onlyimportant in association with the entire assembly, but each individualelement separately represents a decisively important feature.

What we claim is:

1. A vertically adjustable, warpproof black-board suitable for shippingin the form'of its component parts for easy assembly at the place ofuse, which comprises, in combination, a coated asbestos panel; a sheetmetal backing on said panel; a first frame at the rear of said panel:

plus backing; said panel backing and first frame. constituting theassembled first component part; a second component part, readilyassembledtogether with saidfirst component part and other minor parts atthe. place of use constituting a second. frame comprising a T-bar as top1 member; an angle bar as bottom member; said bars be ing connected attheir ends each by a Z-bar which also serves as a guide rail; a pair ofslide bars attached to said angle bar; means for maintaining therectangular shape of said second frame; a blackboard carrier holding thevassembled blackboard; at least one pair of two-armed clamping leversdisposed one above the other, each of them pivotably rotatable, one armof each being bentat right angles; a guide roller being disposed on saidarm and moving within said guide rail; the other lever arm beingprovided with a recess at its free end; spring means, coacting with aclamping screw and nut thereon, disposed in said recess and regulatingthe pressure on said guide roller which thus is urged elasticallyagainst said guide rail; light-weight containers to be filled with aheavy finely grained substance upon assembly to act as counterweightsand facilitate the vertical movement of said panel;

and sprocket and bearing means for said counterweight.

2. The blackboard as defined in claim 1, wherein said means =formaintaining the rectangular shape are gusset plates, one on each cornerof said second frame; said .gusset plates being welded to said Zbars andconnected .to the upper and lower members by at least two nuts and boltseach; and staggered with respect to each other.

3. The blackboard as defined in claim 1, wherein said panel has athickness of substantially 2.2 mm. and said backing a thickness ofsubstantially 0.3 mm.

4. The blackboard as defined in claim .1, wherein said backing consistsof a plurality of metal sheets interconnected by expansion joints.

5. The blackboard as defined in claim 1, wherein said backing sheet ismagnetic thus capable of holding magnets urged onto said panel.

6. The blackboard as defined in claim 1, wherein said panel is coatedwith a baking enamel.

References Cited by the Examiner FOREIGN PATENTS 4/ 195 1 France. 2/1961 Germany.

1 0/ 1956 Great Britain.

3/ 1955 Switzerland.

EUGENE R. CAPOZIO, Primary Examiner. JEROME SCHNALL, Examiner. 20 H. S.SKOGQUIST, Assistant Examiner.

1. A VERTICALLY ADJUSTABLE, WARPPROOF BLACKBOARD SUITABLE FOR SHIPPING IN THE FORM OF ITS COMPONENT PARTS FOR EASY ASSEMBLY AT THE PLACE OF USE, WHICH COMPRISES, IN COMBINATION, A COATED ASBESTOS PANEL; A SHEET METAL BACKING ON SAID PANEL; A FIRST FRAME AT THE REAR OF SAID PANEL PLUS BACKING; SAID PANEL BACKING AND FIRST FRAME CONSTITUTING THE ASSEMBLED FIRST COMPONENT PART; A SECOND COMPONENT PART, READILY ASSEMBLED TOGETHER WITH SAID FIRST COMPONENT PART AND OTHER MINOR PARTS AT THE PLACE OF USE CONSTITUTING A SECOND FRAME COMPRISING A T-BAR AS TOP MEMBER; AN ANGLE BAR AS BOTTOM MEMBER; SAID BARS BEING CONNECTED AT THEIR ENDS EACH BY A Z-BAR WHICH ALSO SERVES AS A GUIDE RAIL; A PAIR OF SLIDE BARS ATTACHED TO SAID ANGLE BAR; MEANS FOR MAINTAINING THE RECTANGULAR SHAPED OF SAID SECOND FRAME; A BLACKBOARD CARRIER HOLDING THE ASSEMBLED BLACKBOARD; AT LEAST ONE PAIR OF TWO-ARMED CLAMPING LEVERS DISPOSED ONE ABOVE THE OTHER, EACH OF THEM PIVOTABLY ROTATABLE, ONE ARM OF EACH BEING BENT AT RIGHT ANGLES; A GUIDE ROLLER BEING DISPOSED ON SAID ARM AND MOVING WITHIN SAID GUIDE RAIL; THE OTHER LEVER ARM BEING PROVIDED WITH A RECESS AT ITS FREE END; SPRING MEANS, COACTING WITH A CLAMPING SCREW AND NUT THEREON, DISPOSED IN SAID RECESS AND REGULATING THE PRESSURE ON SAID GUIDE ROLLER WHICH THUS IS URGED ELASTICALLY AGAINST SAID GUIDE RAIL; LIGHT-WEIGHT CONTAINERS TO BE FILLED WITH A HEAVY FINELY GRAINED SUBSTANCE UPON ASSEMBLY TO ACT AS COUNTERWEIGHTS AND FACILITATE THE VERTICAL MOVEMENT OF SAID PANEL; AND SPROCKET AND BEARING MEANS FOR SAD COUNTERWEIGHT. 